The present invention relates to a fixing apparatus for fixing a developer image onto paper, and more particularly to a fixing apparatus utilizing an inductive heating method.
An image forming apparatus utilizing a digital technology, for example, an electronic copying machine has a fixing apparatus for applying a pressure onto a developer image melted by heating, thereby fixing the image onto paper.
The fixing apparatus comprises: a heat roller for melting a developer, for example, a toner; and a pressure roller for applying a predetermined pressure to the heat roller, wherein a predetermined contact width (nip width) is formed in a contact region (nip portion) between the heat roller and the pressure roller. On the paper passing though the nip portion, the developer image on the paper melted by a heat from the heat roller is fixed by a pressure from the pressure roller. In recent years, there has been utilized an inductively driven heating apparatus in which a thin film metal conductive layer is formed at the outside of the heat roller, and the metal conductive layer is heated by utilizing inductive heating.
For example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-295452, there is known a roller which comprises electricity and heat insulating property, the roller being applicable to a roller which is excellent in heat insulating property, which is fast in rising during heating, and which requires elasticity, and a heating apparatus using the roller.
In addition, in Jpn. Pat. Appln. KOKAI Publication No. 2002-213434, there is disclosed a technique for broadening a non-offset region which is a range of a fixing temperature, the technique being capable of sufficiently greatly forming a nip width which is a contact length between a heat roller and a pressure roller in a transport direction of recording paper, and obtaining a fixing image with a good quality on which a toner is sufficiently fused onto the recording paper, and is not released therefrom.
If the nip width formed at the nip portion between the heat roller and the pressure roller is not sufficiently allocated, there is a problem that a good image is not formed.